Web treatment



May 1, 1962 H. A. KAHN ETAL WEB TREATMENT 2 Sheets-Sheet 1 Filed Dec.22, 1958 VACUUM 1 AIR INVENTORS am a ED F 1 WALTER C. AN

BY i

United States Patent corporation of Virginia Filed Dec. 22, 1958, Ser.No. 782,326 6 Claims. (Cl. 118-8) This invention relates to a processand apparatus for coating a web, and more particularly, to a process andapparatus for restricting the application of a coating to a web near itsedge.

Heretofore, in coating a web such as a web of cellophane, polyethylene,polypropylene, polyethylene terephthalate, ru-bber hydrochloride, etc.,it was common practice to apply the coating by using an applicator roll,then subsequently to pass the coated web between pinch rolls to squeezeoff the excess coating fluid and then to cure the coating. The customaryapplicator roll normally applied an excess of coating to the web. Thepinch rolls, through which the web subsequently passed, then adjustedthe thickness of the coating by squeezing excess coating material offthe web. The coated web was then passed through a curing stage.

One of the difliculties that heretofore existed in the process recitedabove pertained to the step of squeezing off the excess coating. In thisstep the excess coating fluid tended to spread out in the nip of thepinch rolls. The liquid contained in said nip spread laterally andflowed over the edge of the web, thereby wetting the outer edge of thepinch rolls. Occasionally, the coating material, upon drying, fouled therolls. Since the coating thickness is predicated on the maintenance ofprecise and fixed dimensions on the pinch rolls, it is necessary to keepthe pinch rolls clean. Any coating material which adheres to the rollsurface changes the thickness dimensions and by such changes, thecoating thickness and texture is alfected.

Although it was known that fouling of the pinch rolls surface could beprevented by maintaining a narrow width of uncoated web on each of itsedges, this could not be effected because .of the lack of a suitablecontrol. This is particularly so Where a narrow margin of a smallfraction of an inch must be maintained on a web traveling at speeds upto two hundred feet per minute andlhigher.

The prior art reveals that several means of control were attempted butthese means were not found to be as successful as desired. One exampleof a remedy that Was attempted was an applicator roll whose length wasshorter than the width of the web being coated. In use, however, thissystem was replete with difliculties in that it required very precisepositioning of the web with respect to the applicator roll to preventthe off-center application of the coating. Width variations in the webcaused this positioning to be extremely diflicult, if not impossible,and on such occasions, particularly when the total width of the web wassuddenly reduced, the liquid was able to flow over the edge of the web.If suflicient latitude be left to account for these width variations inthe web, an excessive amount of uncoated web on each side results and,therefore, increases the amount of necessary scrap.

Another example of a remedy that Was attemped is seen in US. Patent1,826,698 in which an applicator roll larger than the width of the webwas used. A staggered arrangement of doctor blades wipes off the excesscoating fluid located near the edge of the web and the web is thenpassed through pinch rolls. In practice, however, this remedy is alsonot as successful as it may seem because width variations in the webnecessitate edge scraping large areas on each side. Due to the fact thatlarge areas are scraped, a large amount of scrap results. Where no largeallowance is provided, the doctor blades occasionally do notsufliciently remove the fluid, or else do not even come in contact withthe web near its edge and, hence, only an improper wiping can result.

An object of this invention is to provide an improved method andapparatus for coating film. A further object of this invention is amethod and apparatus for coating a web which automatically applies thecoating only to the desired center area portion of said web. A stillfurther object of this invention is a method and apparatus whichautomatically prevents coating material applied to one side of a webfrom flowing onto the uncoated side during the coating operation.Another object of this invention is a method and apparatus whichautomatically prevents undue waste of the coating and the web materialby reason of the fact that the coating is applied only to the usefularea of the web. A further object is to apply a fluid coating so as toleave a substantially uniform narrow band of uncoated web at eachlongitudinal edge. Other objects will in part, be pointed out, and inpart, become apparent to those skilled in the art upon reading the fol--lowing detailed disclosure. 7

It has now been found that to accomplish the objects enumerated above,the coating fluid should be applied only to the central portion of a webby the use of auto-f matically adjustable web edge shields so that uponsubsequent doctoring treatment the excess coating fluid will not flowover the edge of the web. More particularly, this invention utilizes anapplicator roll which is wider than the web to be coated but applicationof the coating fluid does not adhere, corrode or otherwise foul theshields and are of such physical characteristics that they donotwrinkle, distort or otherwise interfere with the passage of the webover the applicator roll.

The shield is fastened to a movable arm actuated by a cylinder or othersuitable operating means and positioned through the action of a sensingdevice which detects the position of the edges of the web and which isalso fas-- tened to the movable arm.

If the web edges shift position due to a general position shift of theweb, or to dimensional changes in the web, or to wrinkling, the shieldsover the ends of the applicator roll shift in a substantially identicalmanner to maintain a substantially uniform clearance between the edgesof the web and the edges of the applied coating composition. Therefore,the application of the coating fluid is limited to only a centrallylocated portion of the web so that uponsubsequent spreading by the pinchrolls the composition spreads only laterally for a distance less thanthe entire width of the film. To further insure against undue lateralspreading, air jets located on the applicator side of each edge of thepinch rolls may be used. These may also be made automaticallyadjustableby mechanically coupling them to the movable shield assembly.Thus, in spite of the occurrence of position shifts, width changes,wrinkles or other similar phenomena, a centrally located coating may beapplied regardless of the width of the web.

The invention can be more aptly described by referenceto theaccompanying drawings, in which:

FIGURE 1 discloses a pictorial view of an embodiment of a device thatmay be used for this invention,

FIGURE 2 discloses a detailed plan view of the edge detector and shieldpositioning device used in the embodiment shown in FIGURE 1, and

FIGURE 3 discloses a side elevational view of the edge.

3 detecting and shield positioning devices shown in FIG- URE 2 taken online 2'2'.

In FIGURE 1, web W is shown with an edge passing through an edgedetector 111. This edge detector relays the signal indicating the exactposition of the edge of the web to a controller 112. Depending upon theneeds of the situation, such as for example, a shifting of the edge ofthe web or of the shield, the controller activates the positioner 113which in turn moves the edge detector and the shield 114 in a movementlateral to the web by coordinating the signal indicating the exactposition of the web with respect to the shield so that a predeterminedamount of edge material is shielded from the applicator roll 115. Thusthe web W will only be coated in a predetermined central area of itssurface. In FIGURE 3, the applicator roll 115 is shown having its loweredge portion dipped into an applicator pan 116 while its upper edgecoats the web. The coated web is then passed through a series of pinchrolls 117 and 118 which aids in controlling the amount of coatingcomposition on the tfilm to that which can pass though the nip of thepinch rolls. Excess coating from the pinch rolls falls back into theapplicator pan.

To prevent undue lateral spreading of the coating composition over theedge of the film, an air jet 119 located at each edge is used. It is tobe understood, however, that this air jet may not be required if a veryspecific control can be had over the manner and degree of area coated.It may also be made automatically adjustable by mechanically coupling itwith the movable edge detecting and shielding device. A coated web W isshown emerging from the treatment between the pinch rolls having acoating thereon which is disposed centrally upon the face of the film.

In FIGURE 2, which shows a top plan view of the edge detector and shielddevice, as well as the applicator roll and also a detailed view of thecontroller and positioning devices, the edge detector is shown as apressure sensitive type edge indicating gauge. This detector 111 isshown mounted upon holder 211 which also is used for the purpose ofholding shield 114. This holder has a joint 212 capable of sliding in amovement lateral to the edge of the web upon slide 213. This slide ismounted upon the web manufacturing or handling machinery at a point andin such fashion that a minimum of vibrational and other extraneousforces will be transmitted to the edge detector and shield devicesliding thereon. Slide 213 is of such length that it will take intoaccount large Width variations of the web being manufactured or handled.

The uncoated web W is shown passing over this edge detector and shieldholder 211 and coming into contact with the unshielded surface ofapplicator I011 115 in passing over it. The applicator roll obtains itscoating from applicator pan 116 as it revolves about its axle 214 drivenby pulley 215.

The edge detector 111, as shown in the figures, is of the pneumatictype. Preferably it operates responsive to the change in flow of gas atrelatively low velocity and relatively low pressure above atmospheric.In addition it is preferably capable of a proportional response to achange in gas flow. This feature is particularly desirable Where the webmoves at high linear velocity as will be more fully pointed out below.

As the edge of the web W passes over opening 215 in the edge detector111, a variation in the pressure in the process line 219 occurs, thepressure being regulated from an outside source, by means of conduit 217having valve 218. This variation in vacuum is detected by controller 112which may operate on the pneumatic"null balance principal described inthe September, 1945, issue of Instruments Magazine (page 598). A sourceof constant pressure, preferably below atmospheric, is supplied to thecontroller by conduit 330 having regulator 331, in order to maintain adesirable reference pressure level.

In the system shown, when a variation in pressure occurs, the controlleractivates the positioner by varying the amount of air pressure suppliedto the positioner through conduit 221. This activating pressure is alsosupplied from an outside source, in this case, through conduit 220. Thispositioning is accomplished by means of the diaphragm and nozzlearrangement in the controller as discussed in the cited articleappearing in Instruments Magazine. Additional pressure, needed for rapidmovement of the piston 225 of the positioner, is supplied throughconduit 222, this line being provided in addition with valve 223, gauge224 and branch lines 226 and 227.

When a movement toward the center of the web is required, the airpressure on the spring side of the piston 225 of the positioner 113 isincreased in response to greater gas flow through controller 112. Ifmovement away from the center of the web is required, the air pressureon both sides of the piston is changed toward a balanced pressure sothat spring 228 may cause such movement.

A more detailed discussion of the positioner can be seen in an articleappearing in the September, 1951, issue of Product Engineering (page151). For transmitting the force of movement of the piston 225 to theedge detector and shield holder, connector rod 229, which connects thepiston to the holder, is used. For the rapid movement of this detectingand shielding combination which is necessary when the edge of filmdetected is traveling at high rates of speed, in excess of one hundredfeet per minute, the construction must be light in weight. The devicehas been found to be suitable for tracking the edge of a cellophane webtraveling at a linear velocity of over two hundred feet per minute andin continuously shielding about one quarter inch of each edge of the webalthough the position of each edge varied by as much as three times thisdistance.

In FIGURE 3 there is shown a detailed side view of the edge detector andshield device taken on line 2'2' of FIGURE 2. As shown, the web W passesbetween the jaws of the detector 111" and 111 and past edge detector111, and then across the shield 114. It is to be noted that the widthdimensions of the shield are over-exaggerated in the view shown. Theedge detector is mounted upon holder 211 which has slidable joint 212 soas to be able to slide upon axle 213. The holder 211 is also used forthe purpose of supporting shield 114 which is also mounted to its body.

The holder 211 is provided with a drip spout 311 for the purpose offacilitating easy return of excess coating solution, deposited upon theshield, to the body of coating composition 312 contained in theapplicator pan 116.

Coating composition is constantly applied to the web W by means ofapplicator roll 115. Coated web W is that portion of the web to theright of the wall 115. After contacting the roll, it is passed throughpinch rolls 117 and 118 where the coating composition is spreadlaterally. Excess coating falls from the pinch rolls back into theapplicator pan.

In operation, the web W is fed to the apparatus to pass its edgesthrough a set of edge detectors to indicate the position of each edge ofthe web. Each detector sends a pressure signal which indicates theposition of the edge of the web to a controller which in turn activatesa positioner. The positioner moves the edge detector and shieldercombination mounted on holder 211 in a lateral movement as required,either to or from the edge of the web.

The shield position relative to the web edge may be adjusted for thepurpose of shielding a certain distance in from the edge of the web,either before or during the coating operation. Once this is done, theweb as it passes over the applicator roll, is coated only in the centralportion of its surface, and hence movement through and treatment by thepinch rolls 117 and 118 will etfect only a lateral spreading of thecoating. The shield position adjustment is such that the spreading willnot cause movement of coating composition beyond a point removed fromthe edge of the web. This prevents undue fouling of the pinch rolls aswell as undesired coating of the underside of the web.

To further effect a desired control of the spreading of the coating, airjets 119 may be located at each edge of the web on the applicator sideof the pinch rolls. These may be made automatically adjustable by mechanically coupling them to the adjustable edge detecting and shieldpositioning device.

While a specific embodiment of an apparatus that may be used in thisinvention has been shown, it is to be understood that other variationsand modifications may be made in the apparatus without departing fromthe spirit and scope of this invention.

The edge detector used in place of the type shown above may consist ofan air jet type detector in which a plurality of air jets are disposedin an array laterally across the edge of the film. These jets can thusbe directed across and against the edge of the film so as to impinge inpart upon a nozzle or receiver opening or openings on the other side ofthe web. Thus, shielding, by the edge of the web, of some of the jetswill give an indication of the position of the edge of the web. Oneessential feature of the subject device and method is that it is capableof detecting the exact position of the web edge and not simply whetherit is shielded or not. Thus, the detection and correction of the extentof shielding is continuous rather than intermittent. This, in additionto a light weight construction and proportional response to change inweb position, is essential to tracking and reliably masking a narrowmargin of each edge of the web simultaneously. Such reliable masking isrequired to minimize the formation of a Waste uncoated edge region oflarge dimensions and at the same time to avoid fouling of the apparatusbeyond the I011 115.

For the controller, the type used in the embodiment shown above is ofthe pneumatic control relay type. The particular apparatus used wasmanufactured by the Moore Company of Philadelphia, Pennsylvania, and isknown as the Moore Nullmatic M/F No. 68WT17. Obviously, other controlrelays may also be used, either in conjunction with the variations ofthe edge detector disclosed above or with other modifications embodyingthe same principles but not here disclosed. Besides this pneumaticcontrol relay, one may also use an electronic circuit type relay inwhich a signal from the edge detector is picked up, converted to aproportional electrical signal, and utilized to activate the positioner.The signal from the edge detector, depending upon whether it is useddirectly in the pneumatic form, or converted proportionally to anelectrical form, would have to be provided for accordingly. It ispreferred to use the pneumatic signal to generate a proportionalresponse for reliability and economy of operation.

The positioner shown in the embodiment of the drawings is made by theCuroflow Corporation of Philadelphia, Pennsylvania. It is to beunderstood, however, that other shield positioners may also be used.

The signal transmitting means between the edge detector, controller, andpositioner may be either pneumatic, electrical, or mechanical, dependingupon the needs of the situation.

With respect to the shield, it may be constructed of any material whichis unaffected by the coating composition and may be flat or curved to anextent depending upon the needs of the situation. One material inparticular is a plastic known as Teflon, or more technically,polytetraethylfluoroethylene. Other materials such as hard rubbersheeting, relatively stifli vinyl sheeting, etc., may also be used.

While a detailed description of this invention has been provided, it isrealized that those skilled in the art may make modifications andadaptations of the process and apparatus described without departingfrom the spirit and scope of the invention. This application is acontinua- 6 tion in part of the application, Serial Number 456,114,filed September 15, 1954, and now abandoned.

Among the alternative modes of practicing the invention are thefollowing:

The detector for the edge of a web which is not subject to large lateraldisplacement relative to the detector may be fixed rather than movable.It may be for example positioned at a web edge location which justprecedes the surface at which the Wfib is to be contacted. A pluralityof orifices such as orifices 99 of FIGURE 1 adapted to deliver gas to acorresponding set of orifices not shown in gas receiving means may beused with such a detector as for example in the opposing jaws 111' and111" of the edge detector 111 of FIGURE 1. One particularly advantageousarrangement of orifices in a detector jaw is one having a longitudinalas well as a lateral separation, for example, in the rectangularplatforms, forming the inner and opposing surfaces of the detector jaws,the orifices may be located along a diagonal of the rectangle or along aline which crosses a line approximating the average position of the webedge, at a relatively small angle of the order of ten degrees. When theorifices are so positioned, a closer control may be maintained over thelocation of the web edge because the orifices have a closer lateralposition than when they are aligned along a line normal to the web edge.This longitudinal spacing increases the efiiciency and accuracy of edgedetection in addition because it materially reduces the flow of gasbetween orifices which are not positioned in direct alignment.

The avoidance of the lateral flow of gas in passing between the jaws ofthe detector is important in reducing the tendency of the device to giveinaccurate readings. Such flow can result in a pressure reading above orbelow that which accurately indicates the true position of the web.

Where rapid lateral movement of a web must be de tected in order to makerapid corrective adjustments in an apparatus, an elongated slit or rowof orifices aligned normal to the web edge are satisfactory fordispensing and receivng a flow of gas between tWo jaws of a detector.

Where the control must be of a finer order, or where other factors mayinterfere with the normal operation of the detector, alignment of twosets of orifices along a diagonal or along a line which is set at asmall angle to the web edge is preferred. Factors which can interferewith pneumatic web edge detection are excessive flutter of the web edge,curve or other distortion of the web edge and the like. These faults canbe accurately de termined as indicated above.

In an alternate scheme for edge detection, the range of proportionalpneumatic signals subject to faults as described above is minimized byrestricting the pneumatic signal to a narrow range of film deviationdefined by two sets of orifices in opposed jaws of the detector head. Inthis instance the detector head generates a 3-level pneumatic signalindicative respectively of a film position in which both jets areobstructed; a position in which only one jet is obstructed; and aposition in which either jet is obstructed. By spacing the jets closetogether with respect to the edge of the film the head may be made verysensitive to small film deviations. However, in view of the narrowspacing of the jets the head must thereupon be made movable and made tofollow the film in order to be adaptable to wider range of edgedeviations without sacrificing either sensitivity or reproducibility ofthe pneumatic signal.

Since many examples of the foregoing procedures and articles may becarried out and made, and since many modifications can be made in theprocedures and articles described without departing from the scope ofthe subject invention, the foregoing is to be interpreted asillustrative only, and not as defining or limiting the scope of theinvention.

We claim:

1. Apparatus for limiting contact of the edge of a moving web with asurface brought into contact with the Web which comprises a relativelythin light Wei continually movable shield disposed between said web edgeand said surface, said shield being mounted for continual lateralmovement with respect to said web ed by a continual positioning means,pneumatic web edge detecting means mounted for lateral movement withsaid shield to continuously detect the web edge p sition before saidsurface is contacted by said web, and means for activating saidpositioning means continually responsive to a signal from said detectingmeans.

2. The apparatus of claim 1 wherein the response of said positioningmeans is proportional to the magnitud of the signal received.

3. The apparatus of claim 1 wherein the pneumatic web edge detectingmeans produces a signal proportional to the lateral displacement of saidweb with reference to said detecting means.

4. In a continuous web coating apparatus comprising a source of coatingcomposition, an applicator roll adapted to rotate to transfer saidcoating continuously from said source to a continuous web passing intocontact with the upper surface of said roll, the improvement whichcomprises shields capable of lateral reciprocal motion and interposed atboth ends of said roll between said roll ends and the edges of said webto prevent transfer of said composition to said web edges, separateautomatic means for the lateral positioning of each of said shieldsresponsive to changes in the lateral positions of said web edges, eachsuch automatic means comprising a sensing means attached to one of saidshielding means for simultaneous lateral movement therewith by apositioning means, said sensing means comprising a housing adapted to beevacuated, the upper surface of said housing being provided with alaterally disposed elongated slit opening adapted to admit gas to saidhousing, the pressure in said housing being detected by a pressuresensing element adapted to detect pressure proportionately above andbelow a null pressure, means for positioning said sens- 8 ing andshielding means laterally of said web edges responsive to a change inpressure in said housing above said null pressure to advance saidshielding and sensing means toward said web edge, and acting responsiveto a change in pressure below said null pressure to retract said meansaway from said web edge.

5. The apparatus of claim 4 wherein the response of said positioningmeans is proportional to the change in pressure detected.

'6. Web edge tracking apparatus for detecting the edge of a webcomprising a detector head mounted for lateral movement relative to theedge of a moving web, positioning means for moving said head responsiveto signals from said detector, said head having two jaws extendingoutwardly therefrom and disposed to provide two opposing faces betweenwhich a web edge may move, said faces having therein two sets oforifices aligned approximately perpendicular to said edge to permit aflow of two jets of gas between said jaws, pressure sensitive means insaid detector for detecting three pressure levels indicativerespectively of a film position in which both jets are obstructed, aposition in which only one jet is obstructed, and a position in whichneither jet is obstructed, said positioning means being adapted to movesaid de tector to bring said edge into lateral registry between saidsets of orifices.

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